Optically pumped atomic diffusion maser with separate pumping and observation regions



Oct. 31, 1967 H. G. ROBINSON 3,350,632

OPTICALLY PUMPED ATOMIC DIFFUSION MASER WITH SEPARATE PUMPING ANDOBSERVATION REGIONS Filed Aug. 25, 1964 5 Sheets-Sheet 1 RE LAMP POWER.6 ggPPLY 7 .7- 7 REOSCILLATOR FOR WEAK 7 ELECTRIC DISCHIARGE HELIUMCIRCULAR POLARIZERIO LAMP k xxx x 6 w CIRCULAR POLARIZED LIGHT SOURCE 20FIG 4 I o CIRCULAR L1 A I OPTICAL *1 P PUMPING SOURCE g S 8. 25EXCITATION v 35 S EXCHANGE RF. 4.s.

OSCILLATOR FOR 43 DISCHARGE mvEfiToR. 5 HUGH G-.ROB|NSON ATTORNEY Oct1967 H G. ROBINSON 3 350,632

. OPTICALLY PUMPED ATOMIC DIFFUSIQN MASER WITH SEPARATE Y PUMPING ANDOBSERVATION REGIONS Filed Aug. 25, 19 64 5 Sheets-Sheet 2 RF FREQUENCYFOR MULTIPLIER DISCHARGE CIRCULAR v POLARIZED 68555 FIG] a I? :5 f I6 5556 23 56 53 e 57 58 j 58 57 LM 1 F DJ 53 RE 53 A osc y l AToR 113 559 ADISCHARGE I N V E NTOR.

HUGH G.ROB|NSON ATTORNEY 3,350,632 1TH SEPARATE 5 Sheets-Sheet :5

RF OSCILLATOR FO R DISCHARGE H. G. ROBINSON PUMPING AND OBSERVATIONREGIONS RF OSCILLATOR FOR DISCHARGE OPTICALLY PUMPED ATOMIC DIFFUSIONMASBR VI Oct. 31, 1967 Filed Aug. 25, 1964 F IG.IO

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FOR ISCHARGE R.F.' OSCILLATOR HUGH G.ROBIN$ON ATTORNEY FIGJK OUTPUT REOSCILLATOR FOR DISCHARGE RF OSCILLATOR FOR DISCHARGE FIG.I5

LIGHT SOURCE LYMAN POLARIZED H. G. ROBINSON 3,350,632 OPTICALLY PUMPEDATOMIC DIFFUSION MASER WITH SEPARATE PUMPING AND OBSERVATION REGIONS 5Sheets-Sheet 4.

LOCK-IN DETECTOR PHASE SHIFT NETWORKS INVENTOR. HUGH G.ROBINSON ATTORNEYOct. 31, 1967 Filed Aug. 25, 19 64 9) H O M M M A B T U P R T U E N I 0E a U H 6 m T 8 R N F W O 8 x v 4 9 D X B 2m A w H m a MLL T R W E W0 JM A T m P 2 R mm im m m Rmm l O D s w W O l O R O 6 T m Wu 8 A 10 2 I FRA LQHR L H G UR U RLO G CAI G F II i! L I m S F F m 5 F O D CP Oct. 31,1967 H. G. ROBlNSON 3,3

OPTICALLY PUMPED ATOMIC DIFFUSION MASER WITH SEPARATE PUMPING ANDOBSERVATION REGIONS Filed Aug. 25, 1964 5 Sheets-Sheet 5 IOI 4 3 I i iOSCILLATOR M I DISCHARGE I I I4 I 103 [02 REFERENCE LOCK-IN A OSCILLATORDETECTOR RF *osclLLAToR us 1 FOR '25 ISCHARGE I INVENTOR SWEEP HUGHG.ROB|NSON GENERATOR 5 4.;

ATTORNEY DETECTOR United States Patent 3,350,632 OPTICALLY PUMPED ATOMICDIFFUSION MASER WITH SEPARA'IE PUMPING AND OBSERVATION REGIONS HughGettyo Robinson, Waltham, Mass., assignor t0 Varian Associates, PaloAlto, Calif., a corporation of California Filed Aug. 25, 1964, Ser. No.391,975 18 Claims. (Cl. 324-) The present invention relates in generalto atomic resonance apparatus and more particularly to an opticallypumped diffusion maser having separate optical pumping and observationregions. Such a maser apparatus is especially useful as a magnetometer,gradiometer, frequency standard, atomic clock, gyromagnetic resonancespectrometer, current regulator, and for other devices.

Heretofore, optically pumped atomic diffusion masers have been proposed.Such diffusion masers are characterized by a buffer gas confiningmechanism for containing the radiating atoms within an observationchamber. Such a maser is proposed by James P. Wittke in the Proceedingsof the IRE, March 1957, in an article entitled, Molecular Amplificationand Generation of Microwaves, pages 291 at 314 et seq. Severedifficulties have been encountered with such proposed maser deviceswherein the active medium was both optically pumped and stored orconfined by a buffer gas for stimulated emission of radiation within acommon region or chamber. It has been found that collisions between theresonant atoms in the nonequilibrium energy state and certain metastableatoms produced by the optical pumping have severely limited the lifetimeof, or excessively perturbed the phase of the radiating atoms. When theradiating lifetime of the atom is short, the Q of the electrical circuitcoupled to the radiating or resonating system must be extremely high,such as for example, 60,000. Such a high Q is extremely difiicult toobtain in practice.

In the present invention separate regions or chambers are provided forpumping and for observation of the atomic resonance such that while theatomic particles are undergoing stimulated emission of radiation,collision of these atoms with other atoms in the metastable state orwith electrons, as produced by pumping, are greatly reduced. In thismanner, the radiating lifetime of the atoms are greatly increasedthereby greatly narrowing the line width of the resonance radiation. Inaddition to the realization of longer lifetimes for the atoms in theobservation or resonance region, the possibility of perturbing the phaserelation of the radiating atoms, in the observation region, is greatlyreduced because such undesired collisions are largely avoided. Bydecreasing the resonance line width of the masing atoms and bydecreasing the possibility of perturbing the phase of the radiatingatoms in the observation region, the Q of the circuit coupled to theresonant atom ensemble may be drastically reduced to very practicallevels such as, for example, Qs of 200 and less. Such low Qs are readilyrealizable in practical circuits, thus making the optically pumpeddiffusion atomic gas maser an extremely practical apparatus.

The principal object of the present invention is the provision of animproved diffusion type atomic gas maser apparatus.

One feature of the present invention is the provision of separateoptical pumping and resonance radiation regions or chambersinterconnected by a small opening which small opening determines thestorage time of the polarized atoms in the resonance chamber, wherebythe resonating atoms may be separated from collisions with certainmetastable atoms and electrons in the pumping region to increase theradiating lifetimes of the resonant atoms.

in their nonequilibrium energy state by means of a combined action ofelectron impact produced by an electrical discharge and resonanceoptical pumping radiation, whereby an extremely efiicient mechanism isobtained for raising the nuclei of the radiating atoms to theirnonequilibrium energy state.

Another feature of the present invention is the same as the precedingfeature wherein the radiating resonance atom is He Another feature ofthe present invention is the provision of a geometrical configurationfor the maser envelope having separate pumping and observation chamberswherein the observation chamber surrounds a central pumping chamber,whereby an optimum geometry is obtained. i

Another feature is the provision of an electrical circuit coupled to thestimulated radiating atoms such circuit having an extremely low Q,whereby extremely wide band operation is obtained.

Another feature of the present invention is the provision of resonanceatoms selected from the group consisting of He H, Hg Rb Cs K and NaOther features and advantages of the present inven tion will becomeapparent upon a perusal of the specification taken in connection withthe accompanying drawings wherein:

FIG. 1 is a schematic diagram of an atomic gas maser incorporatingfeatures of the present invention,

FIG. 2 is an energy diagram depicting the pumping mechanism for thenuclear polarization of the He atom,

FIG. 3 is a top view of an alternative observation and pumping chamberconfiguration for the maser of the present invention,

FIG. 4 is a view of the structure of FIG. 3 taken along line 4-4 in thedirection of the arrows,

FIG. 5 is a schematic circuit diagram maser having a Q multiplyingcircuit,

FIG. 6 is the output circuit diagram for an atomic maser of the presentinvention as utilized for a magnetometer,

FIG. 7 is a schematic diagram of a gradiometer utilizing features of thepresent invention, 1

FIG. 8 is an alternative gradiometer apparatus employing features of thepresent invention,

FIG. 9 is a schematic circuit diagram showing the output circuit portionof a narrow band tunable filter or tunable amplifier incorporatingfeatures of the present invention,

FIG. 10 is a schematic diagram of an alternative maser apparatusutilizing a refrigerated observation chamber,

FIG. 11 is a schematic circuit diagram of a low Q output circuit for themasers of the present invention,

FIG. 12 is an alternative low Q output maser circuit of the presentinvention,

FIG. 13 is a schematic diagram of an atomic hyperfine maserincorporating features of the present invention,

FIG. 14 is a schematic diagram of an alternative two chamber maserapparatus,

FIG. 15 is a schematic diagram of an alternative hyperfine maserapparatus,

FIG. 16 is a schematic diagram of an alternative Zeeman transitionmaser,

FIG. 17 is a schematic diagram of an alternative maser of an atomicstructure incorporating separate electric discharge, polarizing andobservation chambers,

FIG. 18 is a circuit diagram in schematic block diagram form of amagnetic field stabilizing apparatus incorporating features of thepresent invention,

FIG. 19 is a schematic diagram of a current regulator apparatusincorporating features of the present invention, and

FIG. 20 is a schematic line diagram of a gyromagnetic resonancespectrometer utilizing features of the present invention.

Referring now to FIG. 1, there is shown a maser apparatus of the presentinvention. More specifically, a dumbbell shaped container or envelope 1,as of Pyrex, serves to contain an ensemble of gaseous atoms such as, forexample, He at a suitable pressure as of approximately 1 mm. Hg. Thedumbbell chamber 1 serves to provide two separate spherical chambers 2and 3, respectively, as of, for example, 3.5 cm. in diameter connectedby a small diameter diffusion tube 4, as of, for example, 4 mm. insidediameter and 3.5 cm. in length. One end of the diffusion tube 4,preferably the end connecting into the observation chamber 3, contains asmall orifice 5 which determines the geometrical lieftime or, in otherwords, the storage time of the atoms within the observation chamber 3.The geometrical lifetime or storage time is determined by the mean timethat it takes an atom which diffuses through the orifice 5 into thechamber 3 to randomly walk about within the chamber, suffering thousandsof successive gas to gas collisions, and finally find its way back outthrough the orifice 5.

The dumbbell container 1 is immersed in a suitable polarizing magneticfield H such as, for example, that produced by a solenoid 6, or in thecase of a weak field a magnetometer, the earth field in which case thesolenoid 6 is absent. Circularly polarized optical resonance radiationobtained from a He lamp 7 and circular polarizer 10 is shone into thepolarizing chamber 2 with the direction of propagation of the polarizedlight having a substantial component parallel to the direction of astrong component of the polarizing magnetic field H The circularpolarizer 10 can take any one of a number of conventional forms. In apreferred embodiment, the circular polarizer is' preceded by acondensing lens 8 and includes a linear polarizer 9, such as, forexample, a polaroid type HR linear polarizer for the infrared and aquarter wave plate material 11 with axes oriented at 45 to the axis ofthe linear polarizer. A suitable quarter wave plate material 11 iscellophane of 0.001" in thickness.

A weak electrical discharge is excited within the polarizing bulb 2 bymeans of an RF. coil 12 preferably split into two coaxial segmentsdisposed on opposite sides of the bulb such that an alternating R.F.magnetic field is produced inside of the pumping chamber 2. The RF. coil12 is excited from a suitable R.F. oscillator 13 for sustaining theelectric discharge.

A maser output circuit 14 is disposed around the observing chamber 3such that the stimulated emission of radiation from the gaseous atoms ispicked up in the circuit and produces a suflicient amount of interactionback on the ensemble of radiating atoms such as to obtain a coherentstimulated emission of radiation from the entire ensemble of gaseousatoms within the observing chamber 3. In one embodiment, the maseroutput circuit 14 includes an inductor 15 parallel resonated with acapacitor 16 at the resonant frequency of the emission of radiation.Also, the AC. magnetic field H produced by the radiation induced currentin the inductor 15,

v should have a strong component H within the chamber 3 at right anglesto the direction of the polarizing magnetic The pumping mechanism whichresults in the nonequilibrium energy state of the nuclei of the heliumatoms within the observing chamber 3 is as follows:

Referring to the energy level diagram of FIG. 2,

He S is excited by electron impact in the polarizing region or chamber2, the electrons being produced by the weak electric discharge therein.The electron impact produces metastable He S states which are opticallypumped by the circular polarized He resonance radiation. The result ofthe optical pumping is to create a nonequilibrium population of 8 statesfor which the nuclear spins tend to be oriented in the same way.Subsequently, collisions with He S states take place in which theexcited electron is exchanged. The result is that the nuclear spinorientation is transferred to the He S state for which the lifetime, inabsence of the discharge, is very long. For example, a transverserelaxation time (radiation lifetime) for the nuclear spins of the He Sstate of as long as 55 seconds corresponding to a resonance line with of6 10 c.p.s. has been obtained. This value was determined primarily bythe magnetic field in inhomogeneities present.

The transfer of angular momentum from the circularly polarized light tothe metastable He and hence to the ground state of that atom results inan impressively large nuclear polarization of approximately 20 percentat a gas pressure of approximately 1 mm. Hg. The He nuclei, thus,polarized in the presence of the magnetic field are then transported bymeans of the diffusion process through the small diffusion tube 4 andorifice 5 into the separate observation region or chamber 3. Use of theseparate observation chamber 3 avoids the presence of metastable atomsand electrons in the resonance region. Such undesired particles in theresonance region are avoided because such electrons and metastable atomshave relatively short lifetimes. Thus, unless they are regenerated inthe resonance region, as by pumping therein, they are eliminated. Theobservation chamber 3 is shielded from the pumping light and electricdischarge.

On the otherhand, the polarized nuclei when not perturbed by suchmetastable atoms and electrons have lifetimes greatly in excess of onesecond and can be stored for relatively long periods in the radiatingstate within the observation chamber 3.

For example, in the above He maser apparatus described with regard toFIG. 1 and utilizing the dimensions called for therein, the orifice 5was dimensioned of such a small diameter as of 0.1 mm., such that thestorage lifetime at the particular pressure was on the order of 28seconds and the Q of the tuned output circuit 14 Was approximately 200.With these parameters maser oscillation of a power of 5x 10* watts wasobtained at terminals 17 width a resonance line with of 1.6 l0 c.p.s. ina polarizing field H of 32 gauss.

With the above parameters, described with regard to FIG. 1, and that ofa field of 32 gauss, the nuclear resonance frequency of the maseroscillations in chamber 3 were at 103 kc./second. The above power andline width give a fractional RMS frequency fluctuation (AJ Y h which isapproximately 5 l0 /vt for an observation time of t seconds. Thisstability results from fundamental phase fluctuations caused by thermalenergy in the tank circuit and neglects contributions due to magneticfield fluctuations. An order of magnitude decrease in the resonance linewidth is easily obtained to approximately 6 10- c.p.s. with transverserelaxation times of as long as 55 seconds utilizing apparatussubstantially the same as that shown in FIG. 1.

He has the unusual property of being able to undergo many wallcollisions with the containing vessel 3 without appreciable perturbationof its radiating nuclear quantum state. Furthermore, there issignificant motional narrowing of the resonance line because of therelatively fast diffusion of helium through the magnetic field. Thismotional narrowing secures a narrow line width and also produces asymmetrical line shape, even when the magnetic field inhomogeneitydistribution across the sample within chamber 3 is asymmetric. Hence,the output frequency of the He maser is uniquely related to the averagemagnetic field over the sample and the value of the (shielded) Henuclear magnetic moment.

Other atomic species may be utilized for providing the active atomicmaterial for an optically pumped diffusion maser. More specifically,such other materials include Hg Rb 87 and other alkalies. Hydrogen isalso a useful material for producing optically pumped diffusion masers.Masers using such other materials are more fully described below. Itmust be realized that in order to obtain long storage times and longactive lifetimes of the radiating atoms that a significant number ofwall bounces will be obtained in the observation chamber 3 even thoughthe predominant confining mechanism therein is one of buffer gascollisions. Thus, the atom utilized for the active material of the masermust possess qualities which permit it to suffer numerous wall bounceswithout undue perturbation of the stimulated emission of radiation andwithout recombining with the walls or otherwise relaxing. In this regardHg 201 will bounce extremely well while the alkalies as well as hydrogenrequire nonrelaxing inert wall coatings such as Teflon or parafiin. Inthe case of the He atom the stimulated emission of radiation comes fromthe nuclear resonance of 'the helium atom. However, in certain others ofthe above atoms the atomic resonance comes from either the hyperfine orZeeman resonance of the valence electron.

In the case where hyperfine resonance is utilized for a masertransition, such as for the alkalies which includes rubidium, resonanceis obtained from the electron magnetic moment of the atom which isapproximately 1000 times greater in magnitude than the magnetic momentof the nuclei of the atom. Thus, for a hyperfine maser a substantiallyfewer number of atoms, within the observation chamber, will provide astimulated emission of radiation signal of the same order of magnitudeas that produced by nuclear resonance. Thus, one will expect that in thecase of the alkalies and hydrogen, using hyperfine transitions, the gaspressures within the polarizing and observation chambers will besubstantially less than the pressure utilized for helium. Nevertheless,it is contemplated that the predominant confining storage mechanism willstill be one of a buffer gas rather than characterized by a bounce boxstorage mechanism wherein the stored atom makes successive collisionswith the Walls of the container with much less probability of collisionwith other gaseous atoms within the storage chamber, i.e., the mean freepath of the atoms is greater than the transverse dimensions of theconfining chamber.

It should be understood that although FIG. 1 discloses only one pumpingchamber 2 and associated light source, lens and polarizers 7, 8, 9 and11, one or more additional similar pumping chambers and associated lightsources could be coupled by associated diffusion tubes to theobservation chamber 3, if desired. This procedure would enhancepolarization and result in greater output power. Similar considerationsapply to the subsequent embodimerits.

Referring now to FIGS. 3 and 4 there is shown an alternative geometricalconstruction for the maser apparatus of the present invention useful forimproved operation in weak fields such as the earths field. Morespecifically, an improved filling factor is obtained by utilizing acylindrical pumping chamber 18 as of Pyrex surrounded by a toroidalobservation chamber 19. The toroidal chamber is interconnected to thecentral pumping chamber 18 via the intermediary of a plurality ofspoke-like diffusion tubes 21 having orifices 5 thereinas previouslydescribed with regard to FIG. 1 for determining the geometrical lifetimeof the radiating atoms within the storage and observation chamber 19. Asin the previous example a pair of electrodes 22 are disposed at oppositeends of the cylindrical pumping chamber and are excited by RF. energyderived from an RF. source 23 to provide a weak electric glow dischargewithin the pumping chamber. One of the electrodes is apertured to admitcircularly polarized resonance radiation from source 20 for pumping theatoms within the pumping chamber to higher energy states. As in theprevious example the direction of propagation of the circularlypolarized optical radiation is parallel to the direction of the magneticfield. Around the toroidal observation chamber 19 there is wound aninductor 24 which may be parallel resonated with capacitor 25 to formthe output circuit 14 of the maser apparatus.

Referring now to FIG. 5 there is shown an alternative improved maserapparatus of the present invention wherein the output circuit 14includes a Q multiplying circuit for enhancing reception of maseroscillations within the observation chamber 3.

Briefly, the Q multiplying circuit includes a pair of vacuum tubes 26and 27, respectively, series connected to each other such that the plateof the first tube 26 is coupled directly to the cathode of the secondtube 27. The output oscillations of the maser circuit 14 are coupled viaa coupling capacitor 28 and grid bias resistor 29 to the grid of thefirst tube 26 wherein the maser oscillation signals are amplified andappear in the plate circuit of the first tube 26. A parallel connectionof capacitor 31 and resistor 32 is provided in series with the cathodelead of the first tube 26 to provide a cathode to grid self-bias forstabilizing the operating point of the amplifier 26.

The amplified signals of the first tube 26 are applied to the secondtube 27 via the cathode circuit and are amplified therein. The amplifiedsignals appear across the tuned tank circuit 33 of the second amplifiertube 27 The tank 33 is slightly detuned from the expected atomicresonance to provide phase shift at the maser frequency. A portion ofthe amplified and phase shifted output signal from the second tube 27 iscoupled back to the input of the first tube 26 via the intermediary of a90" phase shift network consisting of a coupling capacitor 34 and seriesresistance 35. This combined phase shift of the feedback path anddetuned tank 33 provides a slight positive feedback, just below thelevel of self-oscillation, such that with a slight maser signal maseroscillation is obtained. An RC self-biased network is coupled betweenground and the grid of the second tube 27 to provide stable operation.The self-biased network includes a parallel network of resistance 36 andcapacitance 37 series connected with the grid to ground lead of theamplifier tube 27. Fixed grid bias is obtained via a bias resistor 41from the B+ supply 42.

Tubes 26 and 27 together with their associated electrical network serveto multiply the Q of the maser output circuit 14. The output maseroscillations then appear at output terminals 43. The advantage of usingthe Q multiplying circuit as shown in FIG. 5 is that it will permitmaser oscillations to be observed of atomic gas resonance when the maserconditions are marginal in the absence of the Q multiplying circuit.

Referring now to FIG. 6, there is shown a typical magnetometer apparatusutilizing maser features of the present invention. More specifically,the output circuit of the maser includes the inductor 15 parallelresonated with series capacitors 45 and 46, respectively. Capacitors 45and 46 serve as a voltage divider network for impedance matching into asuitable step up transformer 47. The high voltage secondary of the stepup transformer 47 is coupled into the input of an amplifier 48 foramplifying the maser oscillations at the resonant frequency thereof. Inthe case of nuclear resonance, the maser oscillations typically will beof a relatively low frequency. The frequency depends upon the magnitudeof the magnetic field H being measured. In the earths magnetic field themaser oscillation will be at approximately 2 kc. corresponding to anearths field magnitude of approximately 0.5 gauss. On the other hand ifan electron spin system is utilized as the active medium, such as forexample, that found in hydrogen or rubidium, the

resonance is a hyperfine resonance or an electron resonance and theresonant frequency will be in the order of 1400 mc./sec. for hydrogenand 6800 mc./sec. for rubidium.

In the case where the low frequency resonance is utilized, such as thatobtained by resonance of the nuclei of He it is preferred that afrequency multiplier 49 be coupled to the output of the amplifier 48 formultiplying the resonance signal to one of a higher frequency which willyield the desired degree of precision when measured by a suitablecounter 51. The counter displays and may record the frequency as derivedfrom the output of the frequency multiplier 49. By knowing themultiplying factor of the multiplier 49 the resonance frequency of thenuclei is readily ascertained and this resonance frequency is a directmeasure of the magnetic field intensity H If desired, the counter can bespecially adapted such that the read-out is directly in terms ofmagnetic field intensity.

The extreme spectral purity of the resonance signal obtainable from themaser of FIG. 6 permits unprecedented measurement or control of amagnetic field. Also, the maser output frequency will follow faithfullyalmost instantaneously changes in field. This is true in spite of thehigh Q of the nuclear Zeeman transistion. While FIG. 6 shows the maseras having the dumbbell shaped container geometry, if the magnetometer isto be utilized for measuring Weak fields, such as for example, theearths field, it is preferred that the geometry of FIG. 3 be utilizedsince in that case the filling factor for the magnetometer will beenhanced, as previously described.

Referring now to FIG. 7, there is shown a gradiometer apparatusincorporating features of the present invention. More specifically, acommon pumping chamber 54 contains the active gaseous atoms therein. Thepumping chamber is connected to a pair of observation chambers 55 spacedsome distance from the pumping chamber 54 and separated from each otherby distance D which can be on the order of meters in length. Theobservation chambers 55 are interconnected to the pumping chamber 54 viathe intermediary of elongated diffusion tubes 56 containing orifices 57for determining the geometrical lifetime of the radiating atoms withinthe observation chambers 55. As in the previous examples, the device isfilled with a suitable gas such as He and the pumping chamber 54 isirradiated with circularly polarized light from a suitable source 20,the direction of the light being parallel to the direction of themagnetic field it is desired to measure. In addition, the pumpingchamber contains a weak electrical discharge such that the He nuclei arepolarized as described above with regard to FIG. 1.

A pair of KB. or electromagnetic shields 58, as of copper, are disposedbetween the pumping chamber 54 and the observation chambers 55 toprevent interference between the maser oscillations in the spacedobservation chambers 55. Maser circuits 14, coupled to the spacedobservation chambers 55, provide output signals having frequenciescorresponding to the magnetic field intensities over the respectiveobservation chambers. If there is a gradient in the magnetic field, thenthe maser oscillation frequency from one chamber 55 is slightlydifferent than the maser oscillation frequency from the otherobservation chamber and the difference in frequency is a direct measureof the magnetic field gradient. The two maser signals can be readilycompared in a suitable frequency mixer or lock-in detector to yield adirect output signal which is a measure of the gradient.

The maser output signals from the two observation chambers 55 arepreferably first each supplied to separate pre-amplifiers 53 to preventcoupling and pulling of one maser oscillator by the other. The outputsof the pre-amplifiers 53 are then fed to a mixer 59 where they are mixedto produce a difference frequency which is fed to a frequency counterand suitable gradient display device 60 giving a direct indication ofthe gradient. If desired, greater precision may be obtained bymultiplying the output of the mixer 59 before counting and displaying infrequency counter and display 60 in order to obtain greater precision inthe measurement of the difference frequency, as previously described.

The particular geometry shown in FIG. 7 is especially desirable since itpermits the two observation regions to be fed from a single pumpingchamber.

Referring now to FIG. 8, there is shown an alternative maser apparatusof the present invention. This apparatus is similar to that shown inFIG. 7 with the exception that it is simplified to the extent that onlya single maser circuit is utilized together with a single preamplifier.In this case, atomic particles pumped in the pumping chamber 54, aspreviously described in FIG. 7, diffused through a first diffusion tube56 into a first observation chamber 55 via orifice 57. A certainfraction of the atomic gas particles within observation chamber 55 arepermitted to escape from chamber 55 and diffuse along a second diffusiontube 62 to a second observation chamber 63. Diffusion tube 62communicating between the pumping chamber 55 and the second observationchamber 63 is dimensioned such that the diffusion time through the tube62 is relatively short compared to the radiation time of the atomicparticles. In this manner, the resonant frequency of the particles inthe first observation chamber 55 is determinative of the averagemagnetic field intensity in the chambers 55 and 63. Thus, the averagemagnetic field in chamber 63 can effectively be monitored by the outputmaser circuit 14 without the necessity of using an output circuitdirectly at chamber 63. Thus, the maser resonance signal is detected inthe output maser circuit 14 which is then amplified in the amplifier 64and fed to the counter and indicator 66 as previously described.

Referring now to FIG. 9, there is shown a narrow band tunable filter ortunable amplifier embodiment of the present invention. Morespecifically, there is shown the maser apparatus according to FIG. 1wherein the output circuit 14 has been slightly modified by including aseparate input loop 71 coupled to the observation chamber. Also coupledto the observation chamber is an output loop 72 wherein output signalsare obtained. When the apparatus is operated as a narrow band, tunablefilter or amplifier, the maser parameters of filling factor 1 Q of thetuned output circuit, and polarization M of the atomic resonanceparticles are one or more reduced below the threshold level of sustainedmaser oscillation. In such a case, the particles within the observationchamber are not undergoing coherent stimulated emission of radiationsuch that there is no output signal. However, in the presence of aninput signal applied to observation chamber and the maser tank circuitvia the intermediary of the input loop 71, the input signal if at theresonant frequency of the atoms within the observation chamber, willproduce a stimulation of emission or radiation from the ensemble ofatoms, such emission being coherent and serving to amplify the signalapplied via the input loop 71. The stimulated emission of radiation isthen received in the maser tank circuit and coupled outwardly thereof byoutput loop 72 to a useful load not shown.

The pass band of the device as a filter or amplifier is tuned by varyingthe magnitude of the polarizing magnetic field H by changing the currentin the solenoid 6 or by providing a suitable secondary bucking coil foraltering the total polarizing field over the observation chamber. As anarrow band filter or amplifier the device has extremely narrow bandWidth characteristic of the Zeeman resonance line width on th order of10* cycles per second. As previously stated the center frequency is setby the polarizing magnetic field intensity and tuning of this fieldintensity varies the center frequency of the filter and/or amplifier.The device is capable of following extremely rapid fluctuations in thefield and hence a time programmed center frequency is obtainable whichmay be used for secure communications or the like. The frequencyresponse is Lorentzian. The pass band of the tunable filter or amplifiercan be altered by dimensioning the observation chamber orifice to adjustthe geometric lifetime of the radiating atoms. For example, decreasingthe geometric lifetime within the observation chamber increases the passband of the maser. In addition, the pass band can be increased byincreasing the magnetic field inhomogeneity over the observation chamberor by increasing the temperature of the observation chamber.

The electronic tunable band width of the maser oscillator or amplifiercan be greatly increased by provision of an output circuit 14 which hasa Q on the order of one or less. However, as the Q of the output circuitis decreased, the filling factor 1 and/ or magnetic polarization M ofthe resonance ensemble of atoms must be increased to maintain maserconditions. The filling factor can be optimized, as previouslydemonstrated, by using a toroidal observing chamber geometry. Themagnetization M of the radiating atoms can also be increased by severalmeans, such as: increasing the pumping light flux, increasing thepressure of the active gaseous atoms while maintaining a givenpolarization, or by lowering the temperature of the observation chamberrelative to the temperature of the pumping chamber. This lattertemperature effect permits an increase in the density of the radiatingatoms by the ratio of the absolute temperatures of the two chambers. Forexample, cooling the observation chamber to 77 Kelvin from 300 Kelvinreduce the Q required for oscillation by a factor of approximately 4.The power output is increased by approximately a factor of 16.

If found desirable or necessary to eliminate any possibility of directcoupling between the input circuit 71 and output circuit 72, thesecircuits could be physically oriented, for example, in quadrature, fordecoupling purposes or other shielding means could be employed as wouldbe obvious to those skilled in the art.

Referring now to FIG. 10, there is shown a maser oscillator apparatusemploying features of the present invention wherein the observationchamber 3 is cooled by liquid nitrogen or other refrigerant 73 containedwithin a suitable Dewar 74 to a low temperature such that the outputcircuit can have its Q reduced while maintaining maser oscillation. Insuch a device, the Q can easily be reduced to a Q on the order of one orless yielding a device which is operable over a wide band offrequencies. The resonance line width is still very narrow but theresonance conditions are not so critically dependent upon tuning of theoutput circuit. Thus, by varying the intensity of the polarizingmagnetic field the device is operable over an extremely wide dynamicrange of magnetic field intensities and maser frequencies withoutcorresponding tuning of the output circuit.

Referring now to FIG. 11, there is shown an alternative low Q outputcircuit for a maser oscillator and/or amplifier utilizing features ofthe present invention. More specifically, the output circuit includes aninductor for receiving the emission of radiation and the inductor iscoupled directly to a suitable load 75 via leads 76. In this case, :theinductive reactance of inductor 15 is preferably less than the loadresistance at the maser frequency.

Referring now to FIG. 12, there is shown an alternative embodiment tothe structure of FIG. 11 wherein the inductor 15 is coupled to the load75 via the intermediary of a series variable capacitor 77 and leads 76.Here again, the Q of the output circuit can be on the order of one orless and again it is preferred that the inductive reactance of theoutput circuit at the maser frequency be less than the resistance of theload 75. The variable capacitor 77 is provided for tuning out theinductive reactance of the coil 15. In these output circuits Q isdefined by the ratio of wL/R.

Referring now to FIG. 13, there is shown an atomic hydrogen diffusionmaser utilizing the separate pumping and observation chamber feature ofthe present invention. More specifically, the maser includes a pumpingchamber 81 containing hydrogen gas at a low pressure. The pumpingchamber is connected to an observation chamber 82 via the intermediaryof a diffusion tube 83 and orifice 84 for determining the geometricallifetime of the particles within the observation chamber 82, aspreviously described. The dumbbell shaped gas containing structure isformed of a suitable material, such as, for example, quartz andpreferably lined on the entire interior thereof with an inert materialwhich will not cause excited hydrogen atoms to relax or recombine. Sucha material includes Teflon or parafiin. The dumbbell shaped structure isthen immersed in a very small polarizing magnetic field H as of 100,ugauss and shielded from extraneous magnetic fields in theconvention-a1 manner, not shown.

In the apparatus of FIG. 13, the device is designed to operate on afield independent hyperfine transition of AM=0, AF=1, as indicated inthe energy diagram associated with FIG. 13. In such a case, pumpinglight is shone into the pumping chamber 81 from a polarized light sourceby means of a suitable window 85 such as LiF formed in the side wall ofthe pumping chamber 81. The pumping light is preferably Lyman alpharadiation which is 0' or 1r polarized by conventional polarizingtechniques. As before, a suitable means is provided for sustaining aweak electrical glow discharge within the pumping chamber 81 forproduction of atomic hydrogen atoms.

The observation chamber 82 is surrounded by a suitable cavity resonator86, such as a cylindrical resonator dimensioned for operation in thedominant TE mode at the atomic hydrogen hyperfine resonant frequency,which is approximately 1420 mc. A suitable coupling loop 87, turned forclarity in the figure is coupled to the magnetic fields of the circularelectric mode resonator 86 for coupling maser oscillation signals fromthe cavity 86 to a suitable amplifier and load, not shown. The circularelectric mode cavity 86 is arranged with regard to the direction ofpolarizing magnetic field H such that the alternating magnetic fieldcomponent H of the oscillating TE mode is parallel to the direction ofthe polarizing magnetic field H and is also relatively uniform acrossthe observation chamber 82. As before, the pumping light is applied tothe pumping chamber 81 in a direction which is parallel to the directionof the polarizing magnetic field H The atomic hydrogen diffusion maserof FIG. 13 utilizes a field independent hyperfine transition such thatthe resonance maser oscillation obtained from the output loop 87 may beutilized as a frequency standard or atomic clock signal in theconventional manner.

The presence of H gas within the pumping and obser vation chambers -81and 82, respectively, will not prevent operation of the hydrogen masersince the hydrogen gas operates as an excellent buffer gas for theatomic hydrogen atom. In a preferred embodiment, the operating pressurewithin the dumbbell shaped maser container structure is as low aspossible since with the lowest operable pressure the best magnetic fieldinhomogeneity averaging is obtained due to the higher diffusion velocityof the atomic hydrogen particles. In addition, a much lower pressure ofatomic hydrogen and hydrogen gas is permissible in relation to the Hegas pressure used for the He maser, previously described, since-themagnetic moment of the electron of the hyperfine transition of atomichydrogen is approximately 1000 times greater than the magnetic moment ofthe nucleus of the He atom.

Referring now to FIG. 14, there is shown an alternative to the masercontainer structure of the present inven- 1 1 tion. In this structure,the length of the diffusion tube 83 has been reduced to zero such thatthe observation and polarizing chambers are substantially adjacent eachother and separated only by means of the orifice 84. This has theadvantage of added strength and smaller volume of space occupied by themaser.

Referring now to FIG. 15, there is shown an alternative hydrogendiffusion maser utilizing features of the present invention. This maserincludes the same apparatus as the structure of FIG. 13 and identicalnumbers have been used to describe similar parts. Note, however, thatthis maser is designed for operation on a field dependent hyperfinetransition of AM: 1, AF=1. In such a case, it will be noted that thepumping light is still applied in a direction parallel to the polarizingmagnetic field H but in the observation chamber the alternating magneticfield H of the resonant mode of the resonator is arranged to beperpendicular to the direction of the polarizing magnetic field H Byusing the field dependent hyperfine transition the maser of FIG. 15 isuseful as a magnetometer or magnetic field measuring or sensing device.

Referring now to FIG. 16, there is shown an alternative hydrogendiffusion maser wherein the structure is substantially identical to thatshown in FIG. 1 and the maser is designed for operation of an electronZeeman transition of atomic hydrogen. More specifically, the AM=1, AF=0transition is utilized. The energy diagram is shown and the outputresonant frequency of the output circuit 14 is tuned for resonance ateither one of the Zeeman frequency transitions A or B. These transitionsare magnetic field intensity dependent and thus the apparatus is usefulas a magnetometer or magnetic field intensity sensing device.

Referring now to FIG. 17, there is shown an alternative hydrogen maserapparatus incorporating features of the present invention. In thestructure of FIG. 17 the apparatus is substantially identical to thatshown in FIGS. 13 and 15 with the exception that a third chamber 88 isprovided in communication with the pumping chamber for supporting theweak electrical discharge therein. In this manner, the separatedischarge chamber 88 may be provided with uncoated walls such that thewall coating material will not interfere with proper operation of theelectrical discharge which produces the atomic hydrogen.

Referring now to FIG. 18, there is shown a magnetic field stabilizerutilizing a maser incorporating feature of the present invention. Morespecifically, a magnetic field dependent maser such as that shown inFIG. 1 is disposed within a magnetic field H which it is desired tostabilize. The magnetic field dependent maser output frequency is fed toamplifier 92 wherein it is amplified and fed to one terminal of alock-in detector 93. A frequency synthesizer or reference oscillator 94serves to provide a reference frequency determinative of the magneticfield intensity to which it is desired to stabilize the magnetic field HThe output of the frequency synthesizer 94 is fed to the other inputterminal of the lock-in detector 93 where it is compared to the maserfrequency to obtain a DC. error output signal of a phase and magnitudecorresponding to the departure of the magnetic field from the desiredreference magnitude as determined by the frequency of the frequencysynthesizer. The DC. error signal is then fed to an amplifier 95 whereinit is amplified and thence fed via a phase shifter 96 back via lead 97to a field corrective coil 91 which superimposes its field H upon thefield H, to be stabilized. The phase shifter 96 is adjusted to preventself-oscillation of the closed loop system.

The main field H which it is desired to control, is programmable bytuning the frequency synthesizer 94 to the desired frequency. Again, themaser output frequency faithfully follows rapid changes in the magneticfield intensity in which it is immersed. The band pass limitations ofthe system are set by the pass band characteristics of the closed loopserve system. In certain instances, it may be desirable to have one ormore additional parallel feed back paths including amplifiers and phaseshifters 96 and lower inductance corrective coils 91 having wider bandpass characteristics to reduce field fluctuations to an acceptable levelso that the final high pass, narrow band loop can maintain lock.

Referring now to FIG. 19, there is shown a current regulator apparatusutilizing features of the present invention. More specifically, anatomic gas diffusion maser having separate pumping and observationregions such as shown in FIG. 1 is disposed within the magnetic fieldproduced by a solenoid 101 formed of a conductor, the current in whichit is desired to regulate. A given current through the solenoid 101 willproduce a given magnetic field intensity H which results in a certainmaser oscillation frequency. The maser signals are coupled from themaser into amplifier 102 wherein the signals are amplified and thencefed to one input terminal of a lock-in de tector 103. As in the case ofthe magnetic field stabilizer or regulator of FIG. 18, a referenceoscillator or frequency synthesizer 104 produces a reference frequencycorresponding to a given desired magnitude of current through thecircuit to be regulated which includes the inductor 101 as a partthereof.

The reference frequency signal derived from reference oscillator 104 isfed to the other input terminal of the lock-in detector 103 wherein itis compared with the maser oscillation frequency to produce a DC. outputerror signal. The error signal is then fed to the input terminal ofamplifier 105 wherein it is amplified and fed to the control terminal ofa suitable current control regulator device 106 connected in series withthe current through which the current is to be regulated. A suitablecurrent regulating device would include a power transistor or a vacuumtube.

The regulator 106 serves to increase or decrease the current in thecircuit being regulated in order to bring this current into coincidencewith a magnitude of current determined by the reference frequency of thereference oscillator 104. A plurality of magnetic permeable shields 167enclose the coil 101 and maser to prevent external magnetic fieldinfluences from disturbing the desired current regulation. Suitablemagnetic shield materials include soft iron and permaloy.

Referring now to FIG. 20, there is shown a gyromagnetic resonancespectrometer apparatus utilizing features of the present invention. Morespecifically, a sample of matter which it is desired to investigate isdisposed within a sample vial 111 and immersed within a polarizingmagnetic field H such as produced by a superconducting solenoid 112. Asuitable Dewar arrangement is provided at 113 for cooling thesuperconducting solenoid 112 to its superconducting temperature such as,for example, liquid helium temperature. A transmitter coil 114 isdisposed adjacent the sample vial 111 for applying an alternatingmagnetic field component to the sample at right angles to the polarizingmagnetic field H The transmitter signal is derived via amplifier 120from the output circuit of a suitable maser, such as, for example, ahelium maser as described with regard to FIG. 1 where like numerals havebeen utilized to identify similar apparatus.

A receiver coil 115 is disposed with its axis at 90 to the transmittercoil to prevent coupling from the transmitter directly into the receivercoil. Also, the receiver coil 115 is disposed with its axis at rightangles to the polarizing magnetic field H When the transmitter frequencyis at the resonant frequency of the gyromagnetic bodies within thesample of material under analysis gyromagnetic resonance is excited inthe sample and their precession about the polarizing magnetic field Hwill induce a signal in the receiver coil 115. The resonant signalpicked up in the receiver coil 115 is fed to a maser amplifier circuit116, preferably of the low Q type, as previously described with regardto FIGS. 9, 11 and 12.

7 The resonance signals received in receiver coil 115 are amplified inthe maser amplifier over a wide range of frequencies without specialturning of the maser amplifier circuit 116. The maser amplifier circuit116 is coupled to an observation chamber 117 as previously describedwith regard to the amplifier embodiment of FIG. 9. The maser amplifierobservation chamber-117 is coupled to the common pumping chamber 2 viathe intermediary of a diffusion tube 118 and orifice 119.

The resonance signals as amplified by the maser amplifier circuit 116are coupled to the input terminals of "a second amplifier 119 whereinthey are amplified and then detected in detector 121 and thence fed toone terminal of a suitable display device such as oscilliscope andrecorder 122 wherein they are displayed as a function of a sweep signalobtained from sweep generator 123. The sweep generator also serves toprovide a sweep signal to a pair of sweep coils 124 serving to sweep thepolarizing magnetic field intensity over the sample of matter underinvestigation Within the vial 111. An electromagnetic shield 125 as ofcopper is disposed between the two observation chambers 117 and 3 of themaser amplifier and oscillator, respectively, to prevent directelectromagnetic coupling therebetween.

The advantage of utilizing the maser oscillator-amplifier in combinationwith the gyromagnetic sample of matter under investigation is that anextremely precise and self-stabilizing spectrometer apparatus isobtained. More specifically, the transmitter signal has an extremelynarrow line width of on the order of 6X l c.p.s. and likewise the maseramplifier circuit has a line Width of the same order such that themaximum signal-to-noise ratio is obtained. In addition, by disposing themaser oscillator amplifier and sample under investigation in the samepolarizing magnetic field H the transmitter and receiver circuits reactwith the instantaneous minute fluctuations of the polarizing magneticfield in such a way as to compensate for the fluctuations in thepolarizing magnetic field and maintain a precise, stable outputresonance signal.

Since many changes could be made in the above construction of thisinvention andmany apparently widely dilferent embodiment of thisinvention could be made without departing from the scope thereof, it isintended that all matter contained in the above description or shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

1. An atomic resonance apparatus for obtaining regenerative stimulatedemission of atomic resonance radiation including, an envelope structurefor containing a gaseous atomic medium therein at pressures wherein thepredominant gas confining mechanismis one of successive gas to gascollisions, mean-s for constricting diffusion of gaseous atoms from afirst region of said envelope structure to a second region of saidenvelope structure, means for applying optical pumping radiation to saidgaseous medium in a first one of said regions for producing certainnonequilibrium energy states of said gaseous atoms, electrical circuitmeans having the magnetic .fields thereof coupled into said secondregion for electromagnetic interaction with an ensemble of thenonaquilibrium energy gaseous atoms that have diffused from said firstregion into said second region, and the coupling between said electricalcircuit means and said ensemble of gaseous atoms in said second regionbeing sufficiently great such as to produce a net flow of coherent powerat the atomic resonance frequency of said ensemble from said ensemble ofgaseous atoms in said second region to said electrical circuit-means,whereby said radiating ensemble of atoms is removed from the deleteriouselfects of pumping products produced in said first region and wherebysaid circuit means operates independently of the applied optical pumpingradiation, applied in said first region, to monitor atomic resonance ofsaid ensemble of gaseous atoms in said second region.

2. The apparatus according to claim 1 including means for introducinginto said first pumping region atoms excited by an electrical dischargefor interaction with said optical pumping radiation.

3. The apparatus according to claim 1 wherein stimulated emission ofradiation is obtained from the nuclei of the atoms in said secondregion.

4. The apparatus according to claim 2 wherein said gaseous atoms are Heand the radiation in said second region is obtained from the nuclei ofthe atoms making up said ensemble of atoms in said second region.

5. The apparatus according to claim 1 wherein said envelope structure isformed with said second region of the envelope surrounding said pumpingregion whereby a more efficient maser geometry is obtained.

6. The apparatus according to claim 1 wherein said electrical circuitcoupled to said ensemble of radiating atoms has a Q of less than 10,whereby a wide band operation is obtained.

7. The apparatus according to claim 1 wherein said resonance atoms areselected from the group consisting of He hydrogen, Hg and Rb 8. Theapparatus according to claim 1 wherein said electrical circuit is acavity resonator.

9. An optically pumped atomic diffusion maser apparatus including, meansforming an envelope structure, means forming an assemblage of gaseousatoms filling said envelope means to a pressure such that the mean freepath of the atomic particles within said envelope means is substantiallyless than the characteristic transverse dimensions of said envelopemeans whereby said atomic particles travel by diffusion within saidenvelope, means within said envelope for constricting the diifusion ofatomic particles from one region of said envelope to a second region ofsaid envelope, means for producing an electrical discharge in the atomicparticles in said first region thereby placing said atoms in anonequilibrium energy state by means of electron impact, means forirradiating said nonequilibrium energy state atoms produced by saidelectrical discharge with resonance optical pumping radiation to producean overpopulation and polarization of a certain energy state, saidpolarized atoms diffusing through said constricting means into saidsecond region of said envelope for storage therein in the nonequilibriumenergy state, and circuit means disposed adjacent said second region forelectromagnetic interaction with an ensemble of gaseous atoms withinsaid second region in their nonequilibrium energy state for producing anet power flow of coherent emission of radiation from the ensemble inthe second region to said circuit means at the atomic resonancefrequency of the ensemble in the second region, whereby said circuitmeans operates independently of the optical pumping radiation applied insaid first region to monitor atomic resonance of said ensemble ofgaseous atoms in said second region.

10. The apparatus according to claim 9 wherein said gaseous atoms withinsaid envelope means are He atoms and the stimulated emission ofradiation is obtained from the nuclei of the He atoms in said secondregion, whereby an extremely narrow band and precise output signal isobtained the frequency of which is dependent'upon the intensity of thepolarizing magnetic field over the second region.

11. The apparatus according to claim 9 wherein said atoms within saidenvelope are hydrogen atoms and said envelope enclosing said first andsecond regions is coated with a nonrelaxing wall material, saidelectrical circuit means comprises a cavity resonator, and said ensembleof atoms in said second region is radiating from a hyperfine resonancetransition.

12. The apparatus according to claim 11 wherein said first region ofsaid envelope structure includes an uncoated wall portion with theelectrical discharge being predominantly confined to said enveloperegion which is uncoated whereby said coating material does notdeleteriously effect the pumping of the gaseous atoms.

13. The apparatus according to claim 9 wherein said constricting meansis an elongated tube interconnecting said first and second regions, andincluding a second constricting means in said envelope structure forconstricting the diffusion of atomic particles from said one region ofsaid envelope to a third region of said envelope, said polarized atomsdiffusing from said one region through said second constricting meansinto said third region of said envelope for storage therein in thenonequilibrium energy state, and said second and third regions beingspaced apart in space such that the resonant frequency of the stimulatedemission of the atomic particles stored in said second and third regionsis determinate of the resonant conditions in the spaced second and thirdregions.

14. The apparatus according to claim 13 wherein said second and thirdregions are disposed on opposite sides of said first pumping region, andsaid radiating atoms radiate from a transition which is magnetic fielddependent thereby yielding two atomic resonant signals determinative ofthe magnetic fields over said second and third regions, and includingmeans for comparing the two resonant frequencies to obtain a measure ofthe magnetic field gradient between said second and third regions.

15. The apparatus according to claim 9 wherein means are provided forrefrigerating said second region of space relative to said first pumpingregion whereby enhanced stimulation of radiation is obtained.

16. An optically pumped atomic diffusion maser apparatus for currentcontrol including, means forming an envelope structure, atomic gaseousmaterial filling said envelope structure to diffusion pressures, meansdisposed in said envelope for confining diffusion of gaseous atoms froma first region of said envelope to a second region of said envelope,means for exciting an electrical discharge in a first one of saidregions, means for optically pumping said first region to producegaseous atoms in a nonequilibrium energy state for diffusion into saidsecond region, electrical circuit mean-s coupled to the assemblage ofatoms in said second region for exciting stimulated emission ofradiation therefrom and picking up the resonance signal therefrom, meansforming an electrical circuit the current in which it is desired toregulate, means forming a current control device connected in circuitwith the circuit to be regulated, said circuit to be regulated includinga coil portion for generating a magneti field permeating said secondregion of said envelope structure whereby the atomic radiation frequencyis responsive to the magnetic field intensity produced by the currentflowing through said circuit to be regulated, means forming a referencefrequency determinative of the magnitude of the current to be regulatedin said circuit,

means for comparing the reference frequency with the frequency of thestimulated emission from said gaseous atoms to produce an error signal,and means for applying the error signal to said current control devicefor regulating the current in said circuit whereby an extremely stableand precise control of the current is obtained.

17. An optically pumped atomic diffusion gas maser apparatus forgyromagnetic resonance spectroscopy including, means forming an envelopemeans filling said envelope structure with an atomic gaseous medium todiffusion pressures, confining means for constricting the diffusion ofgas within said envelope and subdividing said envelope structure intofirst, second and third regions, means for exciting said gaseous atomsto a nonequilibrium energy state in a first of said regions with saidexcited atoms diffusing into said second and third regions, circuitmeans coupled to a magnetic field dependent atomic resonance of saidexcited atoms in said second region for producing stimulated emission ofradiation at the atomic resonance frequency, means for holding a sampleof matter to be investigated within a magnetic field permeating saidsecond and third regions and said sample of matter under investigation,means for applying the emission of radiation from said second region tosaid sample of matter under investigation to excite resonance there-of,means for detecting resonance of said sample of matter and for applyingthe resonance signal to said third region of said envelope toproducestimulated emission of radiation of said atoms in said third region andto amplify the resonance signals, means for sweeping the resonancecondition of said sample of matter relative to the resonance conditionsof said second and third regions, and means for displaying the resonancesignal of said sample of matter under investigation as a function of thesweep of the resonance condition to obtain an extremely precise andstable resonance spectrum of the sample under investigation.

18. An atomic resonance apparatus for obtaining atomic resonance ofgaseous atomic material including an envelope structure for containing agaseous atomic medium therein at pressures wherein the predominant gasconfining mechanism is one of successive gas to gas collisions, meansfor constricting diffusion of gaseous atoms from a first region of saidenvelope structure to a second region of said envelope structure, meansfor applying optical pumping radiation to said gaseous medium in thefirst one of said regions for producing certain nonequilibrium energystates of said gaseous atoms, means forming an electrical circuit havingthe magnetic fields thereof when energized coupled into said secondregion for electromagnetic interaction with an ensemble ofnonequilibrium energy gaseous atoms that have diffused from said firstregion into said second region and providing means operatingindependently of the optical pumping radiation applied in said firstregion for monitoring atomic resonance of said ensemble of gaseous atomsin said second region, whereby said resonant ensemble of atoms in saidsecond region is removed from the adverse effects of pumping productsproduced in said first region.

References Cited UNITED STATES PATENTS 2,884,524 4/1928 Dicke 324-.52,994,836 8/1961 Holloway 324-.5 3,049,662 8/1962 Abragam et al. 324-.53,206,671 9/1965 Colgrave et al. 324.5

FOREIGN PATENTS 670,586 9/1963 Canada.

OTHER REFERENCES Carpenter: Physical Review, vol. 46, Oct. 1, 1934, pp.607 to 610.

Colgrave et al.: Physical Review, vol. 132, No. 6, Dec. 15, 1963, pp.2561 to 2563, and pp. 2565 to 2568, and p. 2572.

Shearer et al.: The Review of Scientific Instruments, vol. 34, No. 12,December 1963, pp. 1363 to 1366.

RUDOLPH V. ROLINEC, Primary Ex'aminer.

MAYNARD R. WILBUR, WALTER L. CARLSON,

Examiners. M, J, LYNCH, Assistant Examiner,

1. AN ATOMIC RESONANCE APPARATUS FOR OBTAINING REGENERATIVE STIMULATEDEMISSION OF ATOMIC RESONANCE RADIATION INCLUDING, AN ENVELOPE STRUCTUREFOR CONTAINING A GASEOUS ATOMIC MEDIUM THEREIN AT PRESSURES WHEREIN THEPREDOMINANT GAS CONFINING MECHANISM IS ONE OF SUCCESSIVE GAS TO GASCOLLISIONS, MEANS FOR CONSTRICTING DIFFUSION OF GASEOUS ATOMS FROM AFIRST REGION OF SAID ENVELOPE STRUCTURE TO A SECOND REGION OF SAIDENVELOPE STRUCTURE, MEANS FOR APPLYING OPTICAL PUMPING RADIATION TO SAIDGASEOUS MEDIUM IN A FIRST ONE OF SAID REGIONS FOR PRODUCING CERTAINNONEQUILIBRIUM ENERGY STATES OF SAID GASEOUS ATOMS, ELECTRICAL CIRCUITMEANS HAVING THE MAGNETIC FIELDS THEREOF COUPLED INTO SAID SECOND REGIONFOR ELECTROMAGNETIC INTERACTION WITH AN ENSEMBLE OF THE NONAQUILIBRIUMENERGY GASEOUS ATOMS THAT HAVE DIFFUSED FROM SAID FIRST REGION INTO SAIDSECOND REGION, AND THE COUPLING BETWEEN SAID ELECTRICAL CIRCUIT MEANSAND SAID ENSEMBLE OF GASEOUS ATOMS IN SAID SECOND REGION BEINGSUFFICIENTLY GREAT SUCH AS TO PRODUCE A NET FLOW OF COHERENT POWER ATTHE ATOMIC RESONANCE FREQUENCY OF SAID ENSEMBLE FROM SAID ENSEMBLE OFGASEOUS ATOMS IN SAID SECOND REGION TO SAID ELECTRICAL CIRCUIT MEANS,WHEREBY SAID RADIATING ENSEMBLE OF ATOMS IS REMOVED FROM THE DELETERIOUSEFFECTS OF PUMPING PRODUCTS PRODUCED IN SAID FIRST REGION AND WHEREBYSAID CIRCUIT MEANS OPERATES INDEPENDENTLY OF THE APPLIED OPTICAL PUMPINGRADIATION, APPLIED IN SAID FIRST REGION, TO MONITOR ATOMIC RESONANCE OFSAID ENSEMBLE OF GASEOUS ATOMS IN SAID SECOND REGION.